Community Structure, Abundance and Potential Functions of Bacteria and Archaea in the Sansha Yongle Blue Hole, Xisha, South China Sea.

Hui He,Qian Liu,Liang Fu,Naishuang Bi,Lulu Fu,Zuosheng Yang,Yu Zhen

doi:10.3389/fmicb.2019.02404

Abstract

The Sansha Yongle Blue Hole is the deepest blue hole in the world and exhibits unique environmental characteristics. In this paper, Illumina sequencing and qPCR analysis were conducted to obtain the microbial information in this special ecosystem. The results showed that the richness and diversity of bacterial communities in the hole was greater than those of archaeal communities, and bacterial and archaeal communities were dominated by Proteobacteria and Euryarchaeota, respectively. Temperature and nitrate concentration significantly contributed to the heterogeneous distribution of major bacterial clades; salinity explained most variations of the archaeal communities, but not significant. A sudden increase of bacterial 16S rRNA, archaeal 16S rRNA, ANAMMOX 16S rRNA, nirS and dsrB gene was noticed from 90 to 100 m in the hole probably due to more phytoplankton at this depth. Sulfur oxidation and nitrate reduction were the most abundant predicted ecological functions in the hole, while lots of archaea were predicted to be involved in aerobic ammonia oxidation and methanogenesis. The co-occurrence network analysis illustrated that a synergistic effect between sulfate reduction and sulfur oxidation, and between nitrogen fixation and denitrification, a certain degree of coupling between sulfur and nitrogen cycle was also observed in the hole. The comparisons of bacterial and archaeal communities between the hole and other caves in the world (or other areas of the South China Sea) suggest that similar conditions are hypothesized to give rise to similar microbial communities, and environmental conditions may contribute significantly to the bacterial and archaeal communities.

Highlights

Anchialine caves are unique geomorphological units found on karst, volcanic islands and peninsular coastlines around the world that are mostly isolated from each other and have high scientific research and social value
Good’s coverage ranged from 98.75 to 99.85%, indicating that the bacterial 16S rRNA gene sequences retrieved from these 14 seawater samples represented the majority of the bacterial communities in the studied areas
The highest bacterial richness was found in YL0m, while the lowest bacterial diversity was observed in YL150m

Summary

Introduction

Anchialine caves are unique geomorphological units found on karst, volcanic islands and peninsular coastlines around the world that are mostly isolated from each other and have high scientific research and social value. Many anchialine caves were formed during the Quaternary period (approximately 2.5 million years ago to present) because of cyclical sea-level changes (Mylroie and Mylroie, 2011; Pérez-Moreno et al, 2016). These anchialine caves can be hundreds to thousands of years old and contain detailed records of environmental change and landscape evolution (Sullivan et al, 2016). Little or no photosynthetic oxygen production, stratified water columns and restricted vertical mixing contribute to the anoxic or micro-oxic environment and hydrogen sulfide in anchialine caves (Iliffe, 2000; Seymour et al, 2007; Becking et al, 2011; Gonzalez et al, 2011)

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